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2.1. Multipath Device Identifiers
Each multipath device has a World Wide Identifier (WWID), which is guaranteed to be globally unique and unchanging. By default, the name of a multipath device is set to its WWID. Alternately, you can set the user_friendly_names option in the multipath configuration file, which causes DM-Multipath to use a node- unique alias of the form mpathn as the name. For example, a node with two HBAs attached to a storage controller with two ports via a single unzoned FC switch sees four devices: /dev/sda, /dev/sdb, /dev/sdc, and /dev/sdd. DM-Multipath creates a single device with a unique WWID that reroutes I/O to those four underlying devices according to the multipath configuration. When the user_friendly_names configuration
option is set to yes, the name of the multipath device is set to mpathn. When new devices are brought under the control of DM-Multipath, the new devices may be seen in two different places under the /dev directory: / dev/mapper/mpathn and /dev/dm-n.
• The devices in /dev/mapper are created early in the boot process. Use these devices to access the multipathed devices, for example when creating logical volumes.
• Any devices of the form /dev/dm-n are for internal use only and should never be used.
For information on the multipath configuration defaults, including the user_friendly_names configuration option, see Section , Configuration File Defaults. You can also set the name of a multipath device to a name of your choosing by using the alias option in the multipaths section of the multipath configuration file. For information on the multipaths section of the multipath configuration file, see Section, Multipaths Device Configuration Attributes.